Iron is one of the most abundant elements found in the Earth's crust. Bacteria residing in marine and freshwater ecosystems are able to generate energy and grow by breathing (respiring) iron in the absence of oxygen, much in the same way human mitochondria generate energy by respiring oxygen. Iron-respiring bacteria are key players in global processes since they feed on organic carbon as a food source and produce carbon dioxide, a greenhouse gas central to global climate change. Iron-respiring bacteria can also transform hazardous pollutants such as radioactive uranium to non-toxic by-products, thereby remediating environments contaminated with radioactivity. Iron-respiring bacteria are also able to produce electricity in fuel cells, an attractive alternative strategy for clean energy solutions. The ability to respire iron is found in nearly all major branches of the bacterial tree-of-life, including several of the most ancient life forms. Bacterial iron respiration may therefore represent one of the earliest forms of respiration to have evolved on early Earth. Ironically, the molecular mechanism of iron respiration is poorly understood. The main goal of the NSF project is to determine the molecular mechanism of microbial iron respiration. Cell walls of iron-respiring bacteria are often composed of two layers, an inner and outer membrane. Iron respiration therefore presents a unique challenge since iron is highly insoluble in water, forming rust particles that are unable to physically contact the respiratory system located inside the cell. To overcome this problem, iron-respiring bacteria place the respiratory system on the cell surface to physically contact solid iron. The surface of iron-respiring bacteria is covered with sulfur and sulfur-producing proteins, an indication that the iron respiratory process is driven by external iron-sulfur (chemical) interactions. A mechanistic understanding of this process will impact a broad range of scientific disciplines by establishing a new link between sulfur chemistry and microbial iron metabolism. The novel connection between the biogeochemical cycles of iron, sulfur and carbon (in a single bacterial cell) will provide a new model for interpreting the global importance of microbial iron respiration, a process suspected to become more prevalent during changing climate conditions.
Broader Impacts The project will also include strong educational and outreach components. The research team consists of faculty, postdoctoral fellows, and PhD and undergraduate students from two complementary disciplines (microbiology and geochemistry) who will combine their expertise to tackle a complex biogeochemical problem. The project will provide the basis for a new generation of scientists with the ability to communicate effectively across traditional discipline lines. A science outreach program will also be developed to expose K-12 students to the microbial world permeating all aspects of our society. The project includes support for a high school science teacher to work in the laboratory each summer and develop hands-on activities, including a "Microbial Sciences Tool Kit" which will be carried back to high school science classroom. The "Microbial Sciences Tool Kit" will focus on questions involving the impact of microorganisms on global climate, bioenergy and bioremediation. The project will develop and integrate new laboratory exercises about microbes, thereby engaging underrepresented students in modern scientific discovery. These activities will aid high school teachers in meeting specific state science curriculum requirements by focusing on climate, bioenergy, and bioremediation topics. Our program will provide scientific expertise and resources for ethnically diverse student bodies, including minorities under-represented in science.
